JPS6359179A - Noise reducer - Google Patents

Abstract

PURPOSE:To obtain the noise reducer of an NTSC composite signal without an expensive frame memory and a chroma inverter by using a 262H+ or -2nH delay line. CONSTITUTION:The noise reducer is constituted of the delay line 9 of 262H+ or -2nH (n=0, 1, 2 and H is one horizontal period) and an adder-subtracter. Herein, the 262H+ or -2nH delay line 9 is used for taking the field correlation of a luminance signal and a chroma signal in the NTSC signal. The field correlation is the highest when n=0 or 262H. The delay line 9 is constituted of a digital memory and a clock thereof can be applied to either case of 3fsc, 4fsc (fsc is a chroma carrier). Thereby, the noise of the luminance and the chroma signals can be reduced without the chroma inverter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 7. The present invention relates to a noise reducer using a memory having a capacity corresponding to a field of view, and its main field of application is a VTR.

[Conventional technology]

BACKGROUND ART Noise reducers that utilize frame-specific processing of video signals have been widely used in broadcasting VTRs and the like. The basic configuration is shown in Figure 2. input video signal V
After converting i into a digital signal by A/D converter 1, there is a delay of one frame [! 2, only the chroma signal is inverted by the chroma inverter 3, and after being added to the original chroma signal by the adder 4, the D/A converter 5 outputs the output video signal VO. Here, the chroma inverter is NTS
This is to compensate for the fact that the phase of the chroma signal in the C signal is inverted every frame.

The configuration of a more general frame noise reducer is shown in FIG. The difference from FIG. 2 is that it is of a feedback type, and a subtracter 6.7 and a level adjuster 8 are present. In this case, the input/output transfer function F is: gain of K-level adjuster 8 (however, 0 × K × 1) S-nilla plus operator τF: 1 frame time (= 1/30 sec). The frequency characteristics are expressed as IFI, as shown in Figure 4 (30
1zj! This becomes a comb-shaped filter in the t1 period. The depth of the comb changes depending on the value of K.

[Problem that the invention seeks to solve]

When the above conventional technology is applied to systems that require low cost, such as home VTRs, there are the following drawbacks: (1) Expensive frame memory is required (2) The chroma inverter is a chroma It inverts only the signal, and requires a complicated circuit to separate it from the luminance signal. (6) A motion detection circuit is required to avoid unnatural images from moving images. All of these add significantly to the cost. It is.

An object of the present invention is to reduce noise in luminance and chroma signals using a field-equivalent memory without a chroma inverter.

[Means for solving problems]

In order to achieve the above object, in the present invention, 262H±2
It is characterized in that the noise reducer is constructed using a delay line of nH (n=0.1, 2.H is one horizontal period) and an adder/subtractor.

[Effect]

Here, the 262H±2nH delay line is used to take the field correlation between the luminance signal and chroma signal in NTSC. Which has the highest field correlation? This is the case when 1=0, that is, 262H. The delay line is composed of digital mesori, and its clocks are 3fεc, 4fsc
(The present invention can be applied to any case where fsc is a chroma subcarrier.

〔Example〕

Hereinafter, the present invention will be explained in detail based on examples.

FIG. 5 shows a television running f: line, where the solid line means the current field and the dotted line means the previous field. It is well known that if one pixel on the nth line of the current field is P, then the pixel approximately one field before, which has a high correlation with this, is A. Here, A represents 262H before P.

Now, the sampling frequency fs is fS=　　　　　fsc The pixel when selected is indicated by O mark in FIG.

From FIG. 6, the horizontal sampling positions of point P and point A coincide, and a high correlation can be expected. This thing is! 'J
This also holds true when a chroma signal such as a TSC signal is modulated. The carrier frequency of the NTSC chroma signal is fsc (25.58 MHz), and the sampling frequency is 3f! ]c, the chroma phase difference between the current sampling point P and the previous point B is 1.2 =exp(J-π). Point A is 262H before point P, and the number of sampling points between them is: 2621 /fa 1/3fsc = 178815 Therefore, the phase difference between point A and point P is 2 exp (-τπ x 178815) = e
yp (-j 2πX 59605 )=axp(-j
2π) and are in phase. That is, there is a high correlation between point A and point P with respect to the modulated chroma signal as well.

The same can be said for the case where fs=41sc.

The point of the present invention is that the luminance signal and chroma signal in the above-mentioned NTSC composite signal are at point P and its 262 points.
Taking advantage of the high correlation between point A, which is before H,
The purpose is to configure a noise reducer using composite signals as they are.

FIG. 7 shows the basic concept of the present invention. The difference from the conventional example shown in FIG. ) delay line 9 is used.

(2) The chroma inverter 3 is unnecessary and there is a great cost advantage when applied to a home VTR. The transfer function F in this case is F =-= 1 + exp (-s j262rH)
i Here, τH: 1 horizontal period (: 63.5 μs), and its gain characteristic IF+ is shown in FIG. 8(a).

When compared with the signal spectrum in FIG. 8(b), the energy center of the luminance signal nfH (n is an integer) and the energy center of the chroma signal (n + 7 ) fn (n=
227, 227±1, 227±2. .・Figure 1 shows a feedback type circuit which is a practical configuration example of the present invention, and the transfer function is as follows, and its frequency characteristic IF+
is as shown in Figure 9. The noise reduction effect changes depending on the value of K (0 x K x 1). When the value of K is increased,
Deterioration of resolution in the vertical direction, blurring of fast-moving parts of moving images, etc. occur, but this can be suppressed to an acceptable level by a nonlinear circuit such as a limiter.

FIG. 10 shows this, in which a nonlinear circuit 10 is present after the level adjuster 8. It is also possible to place the nonlinear circuit 10 before the level regulator 8. In a conventional noise reducer using frame correlation, the time difference between the signals to be correlated is 1730 seconds, and a complicated circuit such as a motion correction detection circuit is required.

On the other hand, the present invention utilizes field correlation, and the time difference between signals for which correlation is taken is about 1/60 second, so that blurring of moving parts can be prevented with a relatively simple processing circuit such as an IJ miter. The same thing can be said if the output delayed by the 1-field delay line 9 in FIG. 1 is connected to the D/A converter 5 and the output video signal vo is obtained.

FIG. 11 shows a feed forward type circuit which is another embodiment of the present invention. K is generally 1/2#
A limiter circuit can be inserted before or after the selected 0 level adjuster 8 to prevent bleeding.

In the embodiment described above, the case where 262H is used as the delay line of the noise reducer for NTSC composite signal was shown, but in general, 262H±2 nH (H=Q, 1 + 2+ ”・) is possible. However, as n increases, the correlation between signals decreases, and the performance of the noise reducer deteriorates.

Furthermore, when using only the luminance signal, it is possible to use a delay of 262H±nH (n'==Q,' + 2・'').If n is an odd number and fs=
In the case of 3 fsc, there is no sampling point 262H±nH earlier, so the closest sampling point is selected.

〔Effect of the invention〕

As described above, according to the present invention, 262H and 2nH
By using a delay line, it is possible to realize a noise reducer for an NTSC composite signal without using an expensive frame memory or chroma inverter.

Furthermore, since field correlation is used, the degree of deterioration is small even for fast-moving images, which is extremely effective in improving the image quality of home VTRs and the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a practical configuration example of the present invention, FIG. 2 is a configuration diagram of a conventional frame noise reducer, and FIG. 6 is a practical configuration example of a conventional frame noise reducer. 4 is a frequency characteristic diagram of the circuit shown in FIG. 3, FIG. 5 is a diagram showing the correlation of pixels on a television scanning line, and FIG. 6 is a diagram of pixels when fa=3 feet. 7 is a block diagram showing the basic configuration of the field noise reducer of the present invention, and FIG. 8 is a block diagram showing the basic configuration of the field noise reducer of the present invention.
Figure 9 is a frequency characteristic and signal spectrum diagram of the circuit in Figure 1. Figure 10 is a frequency characteristic and signal spectrum diagram when a limiter is added to Figure 1. , FIG. 11 is a block diagram showing another embodiment of the present invention. 1...A/D 2...1 frame delay line 3...Chroma inverter 5...D/A 9...1 field delay line 10...Nonlinear circuit I2) Oni et al. 〔υ 68 times 10 mouths 11 l

Claims (1)

[Claims] 1. Input video signal and input video signal of 262±2n
A signal obtained by taking the difference between signals delayed by H (n=0, 1, 2..., H is 1 horizontal period), adjusting the level of the difference using a level adjuster, and subtracting the level-adjusted output from the input video signal. A noise reducer that outputs a video signal. 2. Input video signal and output video signal 262±2n
A signal obtained by taking the difference between signals delayed by H (n=0, 1, 2..., H is 1 horizontal period), adjusting the level of the difference using a level adjuster, and subtracting the level-adjusted output from the input video signal. A noise reducer that outputs a video signal.